1. Field of the Invention
The present invention relates to a modulating apparatus and method, demodulating apparatus and method, and a transmission medium and in particular to a modulating apparatus and method, demodulating apparatus and method, and a transmission medium which are suitable for modulating data for data transmission or recording on a recording medium, and demodulating the modulated code obtained by this modulation so as to reproduce the data.
2. Description of the Related Art
This block coding converts a data sequence to blocks of mxc3x97i bit units (referred to hereafter as data words), and this data word is converted to a code word comprising nxc3x97i bits according to a suitable code rule. When i=1, this code word is a fixed length code. A plurality of values for i can be selected. Thus, a predetermined i may be selected from the range of 1 to imax (maximum of i). The selected value is indicative of a variable length code. This block encoded code is represented by a variable length code (d, k; m, n; r).
Here, i is known as a restriction length, and imax is r (the maximum restriction length). The minimum run d shows the minimum number of consecutive xe2x80x9c0xe2x80x9ds in repeated xe2x80x9c1xe2x80x9ds in a code sequence. The maximum run k shows the maximum number of consecutive xe2x80x9c0xe2x80x9ds in repeated xe2x80x9c1xe2x80x9ds in a code sequence.
In compact discs or mini-discs (trademark) etc., NRZI (Non Return to Zero Inverted) modulation, wherein xe2x80x9c1xe2x80x9d means inversion and xe2x80x9c0xe2x80x9d means non-inversion, is performed on the variable length code obtained above. The NRZI modulated variable length code (hereafter, referred to as a recorded waveform sequence) is then recorded.
Various modulation techniques have been proposed. If the minimum inversion interval of the recorded waveform sequence is Tmin, and the maximum inversion interval is Tmax, to record at a high density in a linear velocity direction, the minimum inversion interval Tmin should be long, that is, the minimum run d should be large. From the clock reproduction aspect, moreover, the maximum inversion interval Tmax should be short, that is, the maximum run k should be small.
For example, one modulation technique used by magnetic disks or magneto-optical disks, etc., is RLL(1-7) code. The parameters of this modulating technique are (1, 7; 2, 3; 2). The minimum inversion interval Tmin is 2(=1+1)T(=(2/3)xc3x972 Tdata=1.33 Tdata). The maximum inversion interval Tmax is 8(=7+1) (=(2/3)xc3x978 Tdata=5.33 Tdata). In addition, a detection window width Tw is 0.67(=2/3) Tdata. For example, the variable length conversion table for the RLL(1-7) code is as follow.
The symbol x in the conversion table is 1 when the next channel bit is 0, and 0 when the next channel bit is 1 (this is also true in the following explanation).
The table 2 is a demodulation table of Table 1 of the RLL (1-7) code.
In this table, a hyphen (-) means a desired bit (1 or 0, as desired)(this is also true in the following explanation)
In the Table 2, the third code sequence xe2x80x9c100 001xe2x80x9d and the fourth code sequence xe2x80x9c100 0001xe2x80x9d of i=2 are combined to obtain xe2x80x9c100 00-xe2x80x9d for the demodulation. However, in this case, worst error propagation during the bit shift error is 6 bits and the worst error propagation during the bit shift error is 5 bits according to Table 2.
However, the RLL(1-7) code can also be produced from the fixed length code. Parameters of the fixed length RLL (107) code is (1, 7; 2, 3; 1) and the minimum inversion interval Tmin becomes 2(=1+1)T when the bit interval of the recording waveform sequence is T. Thereby, the minimum inversion interval Tmin becomes 1.33 (=(2/3)xc3x972) Tdata when the bit interval of data sequence is assumed as Tdata. Moreover, the maximum inversion interval Tmax is 8T(5.33Tdata). In addition, the detection window width Tw is expressed by (m/n)xc3x97T and its value is 0.67 (=2/3)T. Table 3 shows the table of the fixed length RLL (1-7) code. This table is the ISO standard table. An example of the demodulation table of Table 3 is shown in Table 4.
In this table not x00 means any code word of x11, x10, x01, while not x10 means any code word of x11, x01, x00 and not 00x means any code word of 1x, 10x, 01x (this is also true in the following explanation).
This RLL(1-7) code enables replacement of the data words to be converted as shown in Table 5. In this case, the demodulation can be realized on the 1:1 basis as in the case of the Table 3. An example of the demodulation table of table 5 is shown in Table 6.
In this table, not11 means any data word of 00, 01, 10 (this is also true in the following explanation).
When the code limiting the repetition of the minimum run is given to the above variable length RLL (1-7) code as indicated below. Here, the table adding the code to control the minimum run sequence is called the RML (Repeated Minimum run-length Limited Code). The RML (1-7) code shown in Table 7 is generated for the Table 1. An example of the conversion table of Table 7 is shown in Table 8.
xe2x80x9cxxe2x80x9d in the table 7 is determined by a complementary number of the sequential code bits. In this case, the minimum run is repeated up to five times.
Similarly, when the code limiting the repetition of the minimum run can be added as follow to the fixed length RLL (1-7) code. The RML (1-7) code of Table 9 is generated to Table 3 and the RML (1-7) code of Table 11 is generated to Table 5. An example of the conversion table of Table 9 becomes as Table 10, while the conversion table of Table 11 becomes as Table 12. Moreover, the maximum restriction length in Table 10 and Table 12 is 1 or 3.
As explained above, conversion to the code sequence which is restricted appropriately in the repetition of minimum run at the time of modulation can be performed by adding the conversion rule in the table.
However, when the RML code is used in the modulating apparatus utilizing the RLL code, here rises a problem that design of a new apparatus is necessary because there is the code to be added, although the format of the table is the same in the greater part and the circuit configuration is also complicated.
Considering the background explained above, the present invention has been proposed to make unnecessary the design of a new apparatus with a simplified circuit structure by using the code conversion table of the related art in the code conversion table having the additional code to convert the particular code sequence and then converting the particular code sequence.
A modulating apparatus according to the invention is characterized by providing a converting means for converting a code sequence in which the minimum run d after the run-length limited code conversion is repeated for the predetermined number of times to the predetermined code sequence.
A converting method according to the invention characterized by providing a converting step for converting a code sequence in which the minimum run d after the run-length limited code conversion is repeated for the predetermined number of times to the predetermined code sequence.
A transmission medium according to the invention is characterized by transmitting a computer program comprising a conversion step for converting a code sequence in which the minimum run d after the run-length limited code conversion is repeated for the predetermined number of times to the predetermined code sequence.
A converting apparatus according to the invention is characterized by providing a converting means for converting the code sequence in which the maximum run k after the run-length limited code conversion becomes infinite to the code sequence in which the maximum run k becomes finite.
A converting method according to the invention is also characterized by providing a converting step for converting means for converting the code sequence in which the maximum run k after the run-length limited code conversion becomes infinite to the code sequence in which the maximum run k becomes finite.
A transmission medium according to the invention is also characterized by transmitting a computer program providing a conversion step for converting a code sequence in which the maximum run k after the run-length limited code conversion becomes infinite to the code sequence in which the maximum run k becomes finite.
A demodulating apparatus according to the invention is characterized by providing a converting means for converting a code sequence replaced when the minimum run d is repeated to the predetermined code sequence from the run-length limited code sequence.
A demodulating method according to the invention is characterized by providing a converting step for converging a code sequence replaced when the minimum run d is repeated to the predetermined code sequence from the run-length limited code sequence.
A transmission medium according to the invention is characterized by transmitting a computer program comprising a converting step for converging a code sequence replaced when the minimum run d is repeated to the predetermined code sequence from the run-length limited code sequence.
A demodulating apparatus according to the invention is characterized by providing a converting means for converting a code sequence replaced when the maximum run k is infinite to the predetermined code sequence from the run-length limited code sequence.
A demodulating method according to the invention is characterized by providing a converting step for converting a code sequence replaced when the maximum run k is infinite to the predetermined code sequence from the run-length limited code sequence.
A transmission medium according to the invention is also characterized by transmitting a computer program providing a converting step for converting a code sequence replaced when the maximum run k is infinite to the predetermined code sequence from the run-length limited code sequence.
In the modulating apparatus according to the invention, a code sequence is provided in which the minimum run d is repeated after the run-length limited code conversion is converted to the predetermined code sequence.
In the modulating apparatus according to the invention, a code sequence is provided in which the maximum run k becomes infinite after the run-length limited code conversion is converted to the code sequence in which the maximum run k becomes finite.
In the demodulating apparatus according to the invention, a code sequence is replaced when the minimum run d is repeated is converted to the predetermined code sequence from the run-length limited code sequence.
In the demodulating apparatus according to the invention, a code sequence is replaced when the maximum run k is infinite is converted to the predetermined code sequence from the run-length limited code sequence.